Corrosion inhibitors containing nonionic surfactants

ABSTRACT

The invention relates to the use of compounds of the formula (1) 
     
       
         
         
             
             
         
       
     
     in which R 1  is C 1 — to C 29 -alkyl, C 2 — to C 29 -alkenyl, C 6 — to C 30 -aryl or C 7 — to C 30 -alkylaryl, and nonionic surfactants as corrosion inhibitors.

The present invention is described in the German priority application No. 10 2007 041 215.2 filed Aug. 31, 2007, which is hereby incorporated by reference as is fully disclosed herein.

The present invention relates to a process for corrosion inhibition on and in apparatuses for conveying and transporting hydrocarbons in oil production and processing by adding a metal salt of N-acylmethionine and a nonionic surfactant to the corrosive system.

In industrial processes in which metals come into contact with water or with oil/water two-phase systems, there is the danger of corrosion. This is particularly pronounced if the aqueous phase has a high salt content, as in oil extraction and processing processors, or is acidic due to dissolved acid gases, such as carbon dioxide or hydrogen sulfide. The exploitation of a deposit and the processing of oil are therefore not possible without special additives for protecting the equipment used.

Although suitable corrosion inhibitors for oil production and processing have long been known, they are unacceptable in future for offshore applications for reasons relating to environmental protection.

As typical corrosion inhibitors of the prior art, amides, amidoamines or imidazolines of fatty acids and polyamines have an extremely good oil solubility and, owing to poor partitioning, are therefore present only in low concentration in the corrosive water phase. Accordingly, these products must be used at a high dose in spite of their poor biodegradability.

Quaternary alkylammonium compounds (quats) are alternative corrosion inhibitors of the prior art, which also have biostatic properties in addition to the corrosion-inhibiting properties. In spite of improved water solubility, the quats have a substantially reduced film persistence, for example compared with the imidazolines, and therefore likewise lead to effective corrosion protection only in relatively high doses. The strong algae toxicity and the moderate biodegradability are increasingly limiting the use of quats to ecologically insensitive fields of use.

U.S. Pat. No. 4,240,823 describes N-acylmethionine derivatives which are used as growth regulators in the area of crop protection.

JP-A-8 337 562 and JP-A-8 337 563 describe N-acylamino acids and their alkali metal salts, which can also be used as corrosion inhibitors.

JP-A-49 026 145 describes alkali metal salts of N-acylamino acids, which salts can be used as corrosion inhibitors. N-Lauroylglycine sodium salt is mentioned as an example.

A disadvantage of the compounds of the prior art is, however, that their activity at low doses is often not sufficient.

DE-10 2006 002 784 discloses N-acylmethionine ammonium salts which have an excellent effect as corrosion inhibitors and show good biodegradability and reduced toxicity. A disadvantage of these compounds is, however, their complicated preparation and the associated relatively high production costs.

It was an object of the present invention to provide novel corrosion inhibitors which, in combination with improved corrosion protection, also afford improved biodegradability and lower toxicity in comparison with the corrosion inhibitors of the prior art in addition to good water solubility. Furthermore, the novel corrosion inhibitors should be capable of being produced at an economically acceptable price.

It has now surprisingly been found that metal salts of N-acylmethionine as a mixture with nonionic surfactants have an excellent effect as corrosion inhibitors and show good biodegradability and reduced toxicity. Owing to a synergistic effect between the metal salt of N-acylmethionine and nonionic surfactant, the dosages can be substantially reduced in comparison with the prior art, with the result that the novel corrosion inhibitor mixtures are also advantageous economically.

The invention therefore relates to the use of compositions containing metal salts of compounds of the formula (1)

-   -   in which R¹ is C₁— to C₂₉-alkyl, C₂— to C₂₉-alkenyl, C₆— to         C₃₀-aryl or C₇— to C₃₀-alkylaryl, and nonionic surfactants as         corrosion inhibitors.

The invention furthermore relates to a process for inhibiting corrosion on metal surfaces, in particular of iron-containing metals, by adding at least one metal salt of compounds of the formula (1) and a nonionic surfactant to a corrosive system which is in contact with the metal surfaces.

The invention furthermore relates to compositions containing at least one metal salt of a compound of the formula (1) and at least one nonionic surfactant.

The invention furthermore relates to the use of metal salts of compounds of the formula (1) together with nonionic surfactants as metal processing compositions. Here, the compositions according to the invention also afford very good corrosion protection even under strong mechanical load, such as during grinding, cutting and drilling of metal workpieces.

Corrosive systems in the context of this invention are preferably liquid/liquid or liquid/gaseous multiphase systems consisting of water and hydrocarbons which contain corrosive constituents, such as salts and acids, in free and/or dissolved form. The corrosive constituents may also be gaseous, such as, for example, hydrogen sulfide and carbon dioxide.

Hydrocarbons in the context of this invention are organic compounds which are constituents of mineral oil/natural gas, and the secondary products thereof. Hydrocarbons in the context of this invention are also readily volatile hydrocarbons, such as, for example, methane, ethane, propane and butane. For the purposes of this invention, these also include the further gaseous constituents of mineral oil/natural gas, such as, for example, hydrogen sulfide and carbon dioxide.

Preferred surfactants are those which, in a concentration of 0.5% by weight in water, produce a surface tension of this aqueous solution of not more than 55 mN/m, particularly preferably of not more than 50 mN/m and especially not more than 45 mN/m.

In a further preferred embodiment of the invention, R¹ is C₃— to C₂₃-alkyl, C₃— to C₂₃-alkenyl, C₆— to C₂₄-aryl or C₇— to C₂₅-alkylaryl, in particular an alkyl or alkenyl group having 7 to 17 carbon atoms.

The preparation of metal salts of N-acylmethionine is effected by acylation of methionine by means of carboxylic acid chloride or carboxylic anhydride in the presence of a base (e.g. sodium hydroxide). For economic reasons, DL-methionine is preferably used for this purpose, but the pure enantiomeric forms may likewise be used. C₈₋₁₈ alkyl or alkenyl chlorides, such as, for example, octanoyl chloride, decanoyl chloride, dodecanoyl chloride, coconut fatty acid chloride or oleyl chloride, are preferably used for the acylation.

The hydroxides of alkali metals or alkaline earth metals are preferred as the base used for the preparation of the metals salts according to the invention. The hydroxides of Na, K, Ca and Mg are particularly preferred. Accordingly, the metal salts according to the invention are preferably alkali metal or alkaline earth metal salts, in particular Na, K, Ca or Mg salts, of the compounds of the formula 1.

In contrast to DE-10 2006 002 784, the metal salts of N-acylmethionine are present in unneutralized and isolated form and are formulated directly with the anionic surfactants according to the invention to give the corrosion inhibitor mixture according to the invention. As a result, the preparation process for the corrosion inhibitors according to the invention is substantially more economical.

The metal salts of N-acylmethionine according to the invention are obtained as a rule as 10-50% strength solutions in water and are formulated directly with one or more anionic surfactants to give the corrosion inhibitor mixture. For stabilizing the aqueous formulations, alcoholic solvents, such as, for example, methanol, ethanol, propanol, isopropanol, butanol, 2-ethylhexanol, methyl glycol, butyl glycol or butyl diglycol, may be added.

Suitable nonionic surfactants are described below:

Suitable nonionic surfactants are in particular the ethoxylates of long-chain, aliphatic, synthetic or natural alcohols having a C₄— to C₃₀-alkyl radical or alkenyl radical. These may contain from 1 to 25 mol of ethylene oxide. The alkyl chain of the aliphatic alcohols may be linear or branched, primary or secondary, saturated or unsaturated.

The condensates of C₈— to C₂₂-alcohols with from 2 to about 18 mol of ethylene oxide per mole of alcohol are preferred. The alcohol ethoxylates may have a narrow (“Narrow Range Ethoxylates”) or broad homolog distribution of the ethylene oxide (“Broad Range Ethoxylates”). C₉-C₁₅ oxo alcohols having from 2 to 10 mol of EO and C₁₂-C₁₈ fatty alcohols having from 2 to 10 mol of EO are particularly preferred.

Further suitable nonionic surfactants are condensates of ethylene oxide with a hydrophobic base, formed by condensation of propylene oxide with propylene glycol. The hydrophobic moiety of these compounds preferably has a molecular weight of from 1500 to 1800 g/mol. The attachment of ethylene oxide to this hydrophobic moiety leads to an improvement in the water solubility. The product is liquid up to a polyoxyethylene content of about 50% of the total weight of the condensate, which corresponds to condensation with up to 40 mol of ethylene oxide. Commercially available examples of this product class are the Pluronic® brands of BASF and the Genapol® PF brands of Clariant Produkte (Deutschland) GmbH.

Also suitable as nonionic surfactants are condensates of ethylene oxide with a reaction product of propylene oxide and ethylenediamine.

The hydrophobic unit of these compounds consists of the reaction product of ethylenediamine with excess propylene oxide and generally has a molecular weight of from 2500 to 3000 g/mol. Ethylene oxide is added to this hydrophobic unit up to a content of from 40 to 80% by weight of polyoxyethylene and a molecular weight of from 5000 to 11 000 g/mol. Commercially available examples of this compound class are the Tetronic® brands of BASF and the Genapol® PN brands of Clariant Produkte (Deutschland) GmbH.

Polyethylene oxide, polypropylene oxide and polybutylene oxide condensates of alkylphenols are also suitable as nonionic surfactants.

These compounds comprise the condensates of alkylphenols having a C₄— to C₂₄-alkyl group, which may be either linear or branched, with alkene oxides. Compounds having from 2 to 25 mol of alkene oxide per mole of alkylphenol are preferred. Commercially available surfactants of this type are, for example, Igepal® CO-630, Triton® X-45, X-114, X-100 and X-102, and the Arkopal®-N brands of Clariant Produkte (Deutschland) GmbH. These surfactants are referred to as alkylphenol alkoxylates, e.g. alkylphenol ethoxylates.

Polyethylene oxide, polypropylene oxide and polybutylene oxide condensates of tributylphenol or tristyrylphenol are also suitable as nonionic surfactants. Compounds having from 5 to 30 mol of alkene oxide per tributylphenol or tristyrylphenol are preferred.

Fatty acid amides are also suitable as nonionic surfactants.

Fatty acid amides preferably correspond to the formula (2)

-   -   in which R is an alkyl group having 7 to 21, preferably 9 to 17         carbon atoms and each radical R¹ is hydrogen, C₁-C₄-alkyl,         C₁-C₄-hydroxyalkyl or (C₂H₄O)_(x)H, x varying from 1 to 3. The         C₈-C₂₀ fatty acid amides, in particular the corresponding         monoethanolamides, diethanolamides and isopropanolamides, are         preferred.

Further suitable nonionic surfactants are alkyl- and alkenyloligoglycosides and fatty acid polyglycol esters or fatty amine polyglycol esters having in each case 8 to 20, preferably 12 to 18, carbon atoms in the fatty alkyl radical, fatty acid polyglyceryl esters, alkoxylated fatty acid polyglyceryl esters, castor oil alkoxylates, alkoxylated triglycamides, mixed ethers or mixed formyls, alkyloligoglycosides, alkenyloligoglycosides, fatty acid N-alkylglucamides, phosphine oxides, dialkyl sulfoxides and protein hydrolysis products.

The compositions according to the invention can be used alone or in combination with other known corrosion inhibitors. In general, the composition according to the invention is used in an amount such that sufficient corrosion protection is obtained under the given conditions.

Preferred concentrations in which the compositions according to the invention are used are from 5 to 5000 ppm, preferably from 10 to 1000 ppm, in particular from 15 to 150 ppm. The mixing ratio between metal salt of the compound 1 and nonionic surfactant is preferably from 1:9 to 9:1, in particular from 3:7 to 7:3.

Mixtures of the compositions according to the invention with other corrosion inhibitors and/or those of the prior art are also particularly suitable as corrosion inhibitors.

EXAMPLES

General Method for the Preparation of Metal Salts of N-acylmethionine

In a standard stirred apparatus, 1 mol of DL-methionine in 300 ml of water are neutralized with 50% strength aqueous metal hydroxide solution. 1 mol of carboxylic acid chloride is metered into the resulting solution at 15-20° C., the pH being kept at 10-13 by simultaneous metering of 15% strength aqueous metal hydroxide solution. The reaction solution is stirred for a further 3 h at room temperature. The resulting metal salt of N-acylmethionine is characterized by means of the alkali number (AN) and active substance content. Stated percentages are percentages by weight, based on the weight of the salt according to the invention.

Example 1 N-Cocoyl-DL-methionine Sodium Salt (Comparison)

N-Cocoyl-DL-methionine sodium salt having an active substance content of 40% and an AN=65 mg KOH/g was obtained from coconut fatty acid chloride, DL-methionine and sodium hydroxide.

Example 2 N-Oleoyl-DL-methionine Potassium Salt (Comparison)

N-Oleoyl-DL-methionine potassium salt having an active substance content of 40% and an AN=56 mg KOH/g was obtained from oleoyl chloride, DL-methionine and potassium hydroxide.

Example 3 Corrosion Inhibitor Mixture 1

40 g of N-cocoyl-DL-methionine sodium salt from example 1 were mixed with 8 g of coconut fatty alcohol+5 EO, 20 g of butylglycol and 32 g of water.

Example 4 Corrosion Inhibitor Mixture 2

40 g of N-cocoyl-DL-methionine sodium salt from example 1 were mixed with 8 g of C₁₁ oxo alcohol+5 EO, 20 g of butylglycol and 32 g of water.

Example 5 Corrosion Inhibitor Mixture 3

40 g of N-cocoyl-DL-methionine sodium salt from example 1 were mixed with 8 g of C₁₁ oxo alcohol+8 EO, 20 g of butylglycol and 32 g of water.

Example 6 Corrosion Inhibitor Mixture 4

40 g of N-cocoyl-DL-methionine sodium salt from example 1 were mixed with 8 g of C_(14/15) oxo alcohol+4 EO, 20 g of butylglycol and 32 g of water.

Example 7 Corrosion Inhibitor Mixture 5

40 g of N-cocoyl-DL-methionine sodium salt from example 1 were mixed with 8 g of oleyl alcohol+10 EO, 20 g of butylglycol and 32 g of water.

Example 8 Corrosion Inhibitor Mixture 6

40 g of N-cocoyl-DL-methionine sodium salt from example 1 were mixed with 8 g of p-nonyl phenol+4 EO, 20 g of butylglycol and 32 g of water.

Example 9 Corrosion Inhibitor Mixture 7

40 g of N-cocoyl-DL-methionine sodium salt from example 1 were mixed with 8 g of tributylphenol+8 EO, 20 g of butylglycol and 32 g of water.

Example 10 Corrosion Inhibitor Mixture 8

40 g of N-cocoyl-DL-methionine sodium salt from example 1 were mixed with 8 g of tristyrylphenol+10 EO, 20 g of butylglycol and 32 g of water.

Example 11 Corrosion Inhibitor Mixture 9

40 g of N-cocoyl-DL-methionine sodium salt from example 1 were mixed with 8 g of Genapol PN 30 (ethylenediamine+EO+PO), 20 g of butylglycol and 32 g of water.

Example 12 Corrosion Inhibitor Mixture 10

40 g of N-cocoyl-DL-methionine sodium salt from example 1 were mixed with 8 g of diglyceryl oleate, 20 g of butylglycol and 32 g of water.

Example 13 Corrosion Inhibitor Mixture 11

40 g of N-cocoyl-DL-methionine sodium salt from example 1 were mixed with 8 g of castor oil+20 EO, 20 g of butylglycol and 32 g of water.

Example 14 Corrosion Inhibitor Mixture 12

40 g of N-oleoyl-DL-methionine potassium salt from example 2 were mixed with 8 g of coconut fatty alcohol+5 EO, 20 g of butylglycol and 32 g of water.

Example 15 Corrosion Inhibitor Mixture 13

40 g of N-oleoyl-DL-methionine potassium salt from example 2 were mixed with 8 g of C₁₁ oxo alcohol+5 EO, 20 g of butylglycol and 32 g of water.

Example 16 Corrosion Inhibitor Mixture 14

40 g of N-oleoyl-DL-methionine potassium salt from example 2 were mixed with 8 g of C₁₁ oxo alcohol+8 EO, 20 g of butylglycol and 32 g of water.

Example 17 Corrosion Inhibitor Mixture 15

40 g of N-oleoyl-DL-methionine potassium salt from example 2 were mixed with 8 g of C_(14/15) oxo alcohol 30 4 EO, 20 g of butylglycol and 32 g of water.

Example 18 Corrosion Inhibitor Mixture 16

40 g of N-oleoyl-DL-methionine potassium salt from example 2 were mixed with 8 g of oleyl alcohol+10 EO, 20 g of butylglycol and 32 g of water.

Example 19 Corrosion Inhibitor Mixture 17

40 g of N-oleoyl-DL-methionine potassium salt from example 2 were mixed with 8 g of p-nonylphenol+4 EO, 20 g of butylglycol and 32 g of water.

Example 20 Corrosion Inhibitor Mixture 18

40 g of N-oleoyl-DL-methionine potassium salt from example 2 were mixed with 8 g of tributylphenol+8 EO, 20 g of butylglycol and 32 g of water.

Example 21 Corrosion Inhibitor Mixture 19

40 g of N-oleoyl-DL-methionine potassium salt from example 2 were mixed with 8 g of tristyrylphenol+10 EO, 20 g of butylglycol and 32 g of water.

Example 22 Corrosion Inhibitor Mixture 20

40 g of N-oleoyl-DL-methionine potassium salt from example 2 were mixed with 8 g of Genapol PN 30 (ethylenediamine+EO+PO), 20 g of butylglycol and 32 g of water.

Example 23 Corrosion Inhibitor Mixture 21

40 g of N-oleoyl-DL-methionine potassium salt from example 2 were mixed with 8 g of diglyceryl oleate, 20 g of butylglycol and 32 g of water.

Example 24 Corrosion Inhibitor Mixture 22

40 g of N-oleoyl-DL-methionine potassium salt from example 2 were mixed with 8 g of castor oil+20 EO, 20 g of butylglycol and 32 g of water.

Example 25 Corrosion Inhibitor Mixture 23

55 g of N-cocoyl-DL-methionine sodium salt from example 1 were mixed with 2 g of C₁₁ oxo alcohol+5 EO, 20 g of butylglycol and 23 g of water.

Activity of the Compounds According to the Invention as Corrosion Inhibitors

The compounds according to the invention were tested as corrosion inhibitors in the Shell wheel test. Coupons of C steel (DIN 1.1203 with 15 cm² surface area) were immersed in a salt water/petroleum mixture (9:1,5% strength NaCl solution adjusted to pH 3.5 with acetic acid) and exposed to this medium at a speed of 40 rpm at 70° C. for 24 hours. The inhibitor dose was 50 ppm of a 24% solution of the inhibitor. The protection values were calculated from the decrease in the mass of the coupons, based on a blank value.

In the following tables, “comparison 1” designates a commercially available residue amine quat based on dicocosalkyl dimethylammonium chloride, “comparison 2” a commercially available imidazoline salt based on oleic acid diethylenetriamine and “comparison 3” an example from DE-10 2006 002 784 (morpholinium salt of N-cocoyl-DL-methionine, corrosion inhibitor of the prior art).

TABLE 1 (Shell wheel test) Example Corrosion inhibitor ø protection % Comparison 1 Standard quat 28 Comparison 2 Oleic acid DETA imidazoline 70 Comparison 3 Morpholinium salt of N-cocoyl-DL- 75 methionine Comparison 4 from example 1 67 Comparison 5 from example 2 69 26 from example 3 82 27 from example 4 87 28 from example 5 86 29 from example 6 86 30 from example 7 90 31 from example 8 89 32 from example 9 83 33 from example 10 80 34 from example 11 84 35 from example 12 83 36 from example 13 85 37 from example 14 84 38 from example 15 91 39 from example 16 91 40 from example 17 88 41 from example 18 85 42 from example 19 86 43 from example 20 85 44 from example 21 82 45 from example 22 79 46 from example 23 82 47 from example 24 82 48 from example 25 79

As is evident from table 1, the compositions according to the invention have very good corrosion inhibition properties at a very low dose and in some cases even substantially surpass the activity of the inhibitors of the prior art.

In comparison with example 27, example 48 shows that the synergistic effect of the metal salt of N-acylmethionine in combination with a nonionic surfactant decreases at a ratio of >9:1 but is still present.

TABLE 2 Biodegradability (OECD 306) and toxicity (EC₅₀ Skeletonema Costatum) of selected corrosion inhibitors according to the invention Biodegradability Toxicity Example Corrosion inhibitor [%] EC₅₀ [mg/l] Comparison 1 Standard quat 15.2 0.57 Comparison 2 Oleic acid DETA 6.8 0.33 imidazoline 49 from example 4 78.2 30.2 50 from example 5 81.5 35.2 51 from example 10 85.0 87.7 52 from example 23 82.3 120.7 53 from example 24 86.9 116.0

As can clearly be seen from table 2, the compounds according to the invention exhibit improved biodegradability and lower toxicity compared to the comparative examples from the prior art. 

1. A method for inhibiting corrosion on a metal surface, said method comprising contacting said metal surface with a composition comprising a metal salt of the compound (1)

in which R¹ is C₁— to C₂₉-alkyl, C₂— to C₂₉-alkenyl, C₆— to C₃₀-aryl or C₇— to C₃₀-akylaryl, and a nonionic surfactant.
 2. The method of claim 1, wherein R¹ is an alkyl or alkenyl group having 7 to 17 carbon atoms.
 3. The method of claim 1, wherein the metal salt is an alkali metal salt.
 4. The method of claim 1, wherein the nonionic surfactant is an adduct of from 1 to 25 mol of ethylene oxide and an alcohol having a C₄— to C₃₀-alkyl or C₄— to C₃₀-alkenyl radical.
 5. The method of claim 1, wherein the nonionic surfactant is a product of an addition reaction of from 1 to 40 mol of ethylene oxide with a water-insoluble condensate of propylene oxide and propylene glycol having a molecular weight of from 1500 to 1800 g/mol.
 6. The method of claim 1, wherein the nonionic surfactant is obtained by the addition of propylene oxide to ethylenediamine up to a molecular weight of from 2500 to 3000 g/mol, and subsequent ethoxylation up to a molecular weight of from 5000 to 11
 000. 7. The method of claim 1, wherein the nonionic surfactant is an alkoxylated C₄— to C₂₄-alkylphenol.
 8. The method of claim 1, the nonionic surfactant an alkoxylated tributylphenol or tristyrylphenol.
 9. The method of claim 1, wherein the nonionic surfactant is a compound of formula 3

in which R is C₇-C₂₁-alkyl, R¹ in each case is alkyl or hydroxyalkyl having 1 to 4 carbon atoms or (C₂H₄O)_(x)—H x is a number from 1 to
 3. 10. The method of claim 1, wherein a total amount of metal salt to nonionic surfactant is from 5 to 5000 ppm.
 11. The method of claim 1, wherein a weight ratio of metal salt to nonionic surfactant is from 1:9 to 9:1.
 12. The method of claim 1, wherein said composition further comprises a hydrocarbon and said metal surface is an apparatus for conveying and transporting the hydrocarbon.
 13. The method of claim 1, wherein the composition further comprises a metal processing composition.
 14. A composition containing at least one metal salt of a compound of the formula (1)

in which R¹ is C₁— to C₂₉-alkyl, C₂— to C₂₉-alkenyl, C₆— to C₃₀-aryl or C₇— to C₃₀-alkylaryl, and at least one nonionic surfactant.
 15. The composition as claimed in claim 14, wherein a weight ratio of metal salt to nonionic surfactant is from 9:1 to 1:9. 